The 38 Super Automatic was was introduced by Colt in 1929, essentially an update of the older (and obsolete) 38 Automatic. 38 Super is loaded at higher pressure for significantly increased velocity and energy. Ammunition can be chambered in 38 Automatic pistols but must not be used; all 38 Super Automatic ammunition is headstamped "+P" denoting higher pressure. The 38 Super Automatic uses a .900-inch case with a .355-inch bullet, developing a speedy 1240 feet per second with a 125-grain bullet. The case is semi-rimmed and requires a unique and slightly larger frame than the 45 ACP, which has reduced its availability and popularity. Even so, 38 Super Automatic pistols have remained available and are now seeing a resurgence in popularity. — Craig Boddington